1. Field of the Invention
This invention relates, in general, resistance spot welding equipment and, more specifically, to resistance spot welding electrodes.
2. Description of the Prior Art
Resistance spot welding is a process used to join to thin metal sheets together. A spot weld is produced by clamping two thin sheets of metal together under high pressure or force between two axially aligned electrodes and passing an electrical current between the electrodes through the sheets. The high resistance at the interface of the two metal sheets causes heating of the sheets in an area between the contact surfaces or tips of the electrodes. This rapid heating forms a molten zone of metal which, when cooled, forms a solid weld spot or nugget fusing the two metal sheets together at that point.
The electrodes used for form a spot weld are typically constructed of a highly electrically conductive material, such as copper. The size and shape of the electrodes determines the size and shape of the spot weld. The electrodes may have an integral single piece form or, more conventionally, may be constructed of a holder or shank portion which receives a replaceable cap at its upper end. The interior of the electrode and cap is hollow and is provided with coolant flow paths for removing heat generated by the high electrical current passing through the electrode.
During repeated spot welding operations, the electrodes experience considerable deformation at their contact surfaces due to the high clamping pressures and the heat generated by the electrical current passing through each electrode. Such deformation causes the contact surface of the electrodes to spread out or "mushroom" which increases its diameter and decreases the strength of the weld spot. Frequent reshaping or "dressing" of the electrode tip is required to retain the electrode tip in its original size and shape to create the required weld spot. This interrupts the welding operation which lowers overall production and increases labor costs since manual hand operations are typically employed to reshape the electrode tip to its desired shape and diameter.
Thus, it would be desirable to provide a spot welding electrode which overcomes the problems of previously constructed spot welding electrodes. It would also be desirable to provide a spot welding electrode which has increased heat transfer flow to enhance its useful life.